BASS. LI. Cool gas supply of HI-massive local Seyfert galaxies

Abstract

We present neutral atomic hydrogen (HI) imaging observations of 22 HI-rich ($M_{\rm HI} \gtrsim 10^{9.7} M_\odot$), hard X-ray-selected local Seyferts to explore how cool gas is supplied to active galactic nuclei (AGN) hosts. The sample predominantly resides in group-like, gas-rich environments. About 80% (18/22) of the galaxies have HI-detected neighbors, 61% (11/18) of which clearly exhibit strong lopsidedness, one-sided gas tails, and/or gas structures connecting to nearby companion galaxies, suggesting gas exchange histories. We examine the HI size-mass relation and star formation properties of these HI-rich AGN hosts, finding no systematic deviations from known scaling relations. In most cases, our samples are the most massive systems within their respective groups, implying that our sample is more likely to acquire gas rather than lose it. Interestingly, galaxies with more extended HI disks show stronger AGN activity. Considering that extended HI is often associated with external processes, this finding suggests that environmentally accreted gas - through galaxy interactions and gas exchange with neighboring systems - may have played a role in supplying additional fuel to the AGNs in our sample. Notably, the HI extent-AGN activity correlation becomes even tighter for those AGN hosts whose neighboring galaxies are gas poor or lack HI, further supporting externally supplied gas as a fuel source.

Figures (13)

• Figure 1: Hi gas mass fraction of the sample as a function of stellar mass. The red diamonds show our sample with BAT IDs, and the purple squares show the binned mean gas fraction of the entire BASS-Hi-detected sample from single-dish measurements. The black dot points are the xGASS sample Catinella2018, and the black squares and the grey shaded regions represent the binned mean value and the 5$\sigma$ scatter of the same sample, respectively.
• Figure 2: Images of the first four galaxies. The rest of the samples are presented in the appendix \ref{['appendix:continued_mom_maps']}. (Left) The optical color image. The angular and physical scale bar is shown on the bottom right of each panel. (Center) The integrated Hi intensity contours overlaid on the DSS-1 image. The synthesized beam is shown on the upper left of each panel. The contour levels are (the lowest contour level in $\text{cm}^{-2}$ which is presented at the bottom)$\times2^{n}$, where n=0, 1, 2, 3, and so on. Various contour colors are used to reveal the inner stellar structure clearly, and they are not associated with specific column densities. The scale bar shows 50, 100, or 150 kpc at the given distances of each galaxy. (Right) The moment 1 (velocity field) map. The central velocity is listed at the bottom and indicated by a thick line. In the approaching/receding side (blue/red) of the disk, velocities are indicated with solid/dashed lines, with a separation of 40 $\text{km}\;\text{s}^{-1}$, except for NGC 262, ESO353-G009, and NGC 6232, for which are separated by 15 $\text{km}\;\text{s}^{-1}$. The colorbar on the top of the panel is in the unit of km s$^{-1}$. The names of Hi-detected neighbor(s) are noted in blue.
• Figure 3: Hi mass and size scaling relation. The green dots represent $\sim$500 nearby galaxies analyzed by Wang2016. The solid black line shows the best fit of Wang2016’s sample, and grey colors show its 3$\sigma$ and 6$\sigma$ scatters. The errorbars of ${D}_{\rm HI}$ and ${M}_{\rm HI}$ measurements are plotted. The red diamonds represent the sample for this study. Most of our targets follow the scaling relation within a 3$\sigma$ scatter and are clustered in the high ${M}_{\rm HI}$–${D}_{\rm HI}$ regime. The objects that deviate most significantly from the rest of our sample are labeled with their BAT IDs.
• Figure 4: Global star formation properties of the sample. The black solid line shows the scaling relation from Renzini2015_sfms with 3$\sigma$ scatter (shaded area). The background data (greyscale) is from the MPA-JHU catalog Brinchmann2004, where the contours represent 2D histograms corresponding to approximately 30, 100, 300, 500, 700, 800, and 841 thousand galaxies. The purple points represent all the BASS galaxies in which the star formation rate was measured Ichikawa2019. The red diamonds represent our sample, with BAT IDs.
• Figure 5: Hi-to-stellar mass fraction vs. stellar mass for our targets (red diamonds) and their neighbors (blue circles). Panel (a) shows a subsample in which all Hi-detected neighbors are gas poor for their given stellar mass. Panel (b) shows galaxies in which both gas-poor and gas-rich neighbors are observed. Panel (c) shows the cases with only gas-rich neighbors. Panel (d) shows the hosts with no other neighbors with Hi detected in their surroundings. Hi clouds detected in our observations but not visible in the 2MASS $\text{K}_s$-band are shown as triangles. The upper limit on their stellar mass was estimated by converting the 2MASS $\text{K}_s$-band surface brightness limit using the scaling relation from Wen2013, yielding a limit of $10^{6.82}{M}_\odot$. The solid black line represents the scaling relation from the Hi-selected spiral sample in the Hi Parkes All-Sky Survey Catalog Meyer2004Parkash2018ApJ, with the gray shaded area indicating the $1\sigma$ scatter. Background green points show HICAT data; blue points represent Nançay data vanDriel2016; and black squares indicate binned mean values from the xGASS sample Catinella2018, as in Figure \ref{['figure_mhi_mstar']}. Except for group (c), other host galaxies are likely to have acquired gas from their neighbors.